8 GEOLOGICAL MEMOIRS. 



or chlorite. Colour : spotted greyish-green and brown. [Group 6. 

 Hyperite. Eclogite (and garnet-rock), gabbro (smaragdite-gabbro t 

 or diallage-gabbro), and hypersthenite.~\ 



2. Decomposable in hydrochloric acid, and becoming brownish - 

 green cr reddish on heating to a red heat. Augite as the chief 

 constituent, mixed with labradorite, and grey- or bluish-green iron- 

 chlorite ; generally also calc-spar. Colour: green to greenish or 

 blackish. Accessory constituents : iron-pyrites, calc-spar, seldom 

 magnetic pyrites. Weathering : ferruginous, often calcareous clay. 

 [Group 7. Diabasite (Greenstone). Diabase {diabase-slate and 

 aphanite), diabase- or augite-porphyry, and calc-diabase (and 

 schalsteiri).~\ 



b. Without pyroxene. Partly soluble in hydrochloric acid, often 

 with effervescence. Melting easily before the blowpipe into greenish 

 or greenish-yellow glass. Magnetic. Sp. gr. =2*63 to 2*76. Labra- 

 dorite in intimate union with magnetic iron-ore, iron-spar, calc-spar, 

 and iron-chlorit, which often pervades the mass and coats the amyg- 

 daloid kernels and cavities with a green earthy incrustation. Colour : 

 greenish- or reddish-brown, and grey-greenish, to black. Accessory 

 constituents : rubellan, iron-mica : amygdaloids of calc-spar and 

 quartz. Weathering : leather-brown to red-brown, often calcareous 

 clay. [Group 8. Melaphyre (Trap in part). Simple, porphyritic, 

 and amygdaloidal melaphyre.~\ 



2. Suborder. Always decomposable in hydrochloric acid, and generally 

 with effervescence, showing 35 to 55 per cent, of decomposable, 

 and 45 to 65 of undecomposable parts. Sp. gr. = 2'76 to 3*1. 



Black augite, asthe chief constituent, is combined with labradorite 

 or leucite and magnetic iron-ore. Colour : blackish-grey or black. 

 Accessory constituents: chiefly olivine, zeolites, and mica; also 

 calc-spar and apatite. Distinctly and indistinctly mixed. Wea- 

 thering : ochre-yellow to leather-brown, generally calcareous clay. 

 [Group 9. Basaltite (Trap). Dolcrite and dolcrite-lava, ana- 

 mesite, basalt {amygdaloidal basalt and basaltic lava), wacke, 

 leucite-porphyry , nephelin, and trachyte-doleriteJ] 



The relations of minerals, as rock-components, are shown in a 

 Table exhibiting a diagrammatic synopsis of the^principal minerals 

 that enter into the composition of rocks, and so arranged that at a 

 glance the reader is enabled to recognize the principal mineral in any 

 special rock, and the accessory mineral with it in that or any other 

 rock. 



I. CLASTIC ROCKS.— Pseudoclastic Rocks. 



I. Order. The cement or matrix is orthoclase, but never quartz, lime, 

 or iron-ore ; it is crystalline or slaggy. The rocks of this division 

 frequently resemble the simple, but more often the mixed crystalline 

 rocks ; they are generally unstratified, and form the mantle of those 



